Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$89.37	11.203%	$99.3821	$99.38	$99.40	$99.40
Purchase #2	$99.93	8.570%	$108.494	$108.49	$108.50	$108.50
Purchase #3	$174.98	13.825%	$199.171	$199.17	$199.15	$199.20
Purchase #4	$167.54	6.698%	$178.7618	$178.76	$178.75	$178.80
Purchase #5	$223.50	3.599%	$231.5438	$231.54	$231.55	$231.50
Purchase #6	$57.30	8.418%	$62.1235	$62.12	$62.10	$62.10
Purchase #7	$150.56	6.322%	$160.0784	$160.08	$160.10	$160.10
7 purchase totals =	$963.18		$1,039.5546	$1,039.54	$1,039.55	$1,039.60